1. Field of the Invention
This invention relates to thermochromic polyacetylenes useful in temperature-indicator, indicia-display and laser-writing device applications.
2. Description of the Prior Art
Examples of organic polymers which evidence thermochromic properties, that is, evidence a reversible change of color with temperature are rare in contrast to photochromic polymers. Poly[dodeca-5,7-diyn-1,12-diol bis(ethylurethane)], poly-ETCD, has been observed to change reversibly from green to red in the temperature range of 120.degree. to 140.degree. C., as disclosed in U.S.N.T.I.S., AD Rep. 1974, No. 783709/9GA, from Govt. Rep. Announce. (U.S.) 1974, 74 (21), 51 and G. J. Exarhos, W. M. Risen, Jr., and R. H. Baughman, Journal of American Chemical Society, Vol. 98, pp. 481-487, (1976).
U.S. Pat. No. 3,501,297 (Creamens, 1970) describes a mixture of 7,9-hexadecadiyndioic acid and monomethyl ester of 7,9-hexadecadiyndioic acid forming a blue colored image upon electron beam irradiation wherein the blue color can be reversibly converted to a red color by heating above 50.degree. C. and returned to the blue color upon cooling to below 50.degree. C.
Certain diacetylenes capable of forming images on exposure to radiation are described in U.S. Pat. No. 3,822,134 (1974). Mention is made of stabilizing and fixing the resulting image by heating the irradiated diacetylene to a temperature below the melting point wherein the irradiated image permanently changes color.
U.S. Pat. No. 3,999,946 (1976) describes diacetylenes containing at least two conjugated C.tbd.C groups being capable of undergoing irreversible color changes upon thermal annealing or exposure to radiation, and being utilized as integral time-temperature history indicators.
U.S. Pat. No. 3,723,121 (Hauser, 1973) describes a process for laser beam recording utilizing a chromatic polyacetylenic material containing at least two acetylenic linkages in a conjugated system, such that the material is converted by absorption of incident laser radiation to a color which transmits the incident laser beam wherein no further change takes place. However, the process does not describe the use of materials which will undergo this process in a reversible manner, thus extending the utility of such a material in the process, nor is there described any method for selectively storing or erasing the formed image on the materials, which is an important factor in the utility of such materials for laser recording applications.
U.S. application 700,626 (1976) discloses diacetylenes of the formula, RNHOCO--(CH.sub.2).sub.n --C.tbd.C--C.tbd.C--(CH.sub.2).sub.n --OCONHR' where n is at least 1 and R and R' are C.sub.1 -C.sub.12 alkyl, as being liquid phase processable crystalline diacetylene polymers. However, no mention is made of thermochromic properties of the compounds.
German Patents Nos. 1,940,690 (1971), 1,940,691 (1971) and 1,940,692 (1971) describe the use of compounds such as the phenyl, napthyl, n-butyl, cyclohexyl, p-tolyl and p-chlorophenyl urethane derivatives of 2,4-hexadiyn-1,6-diol and 3,5-octadiyn-1,8-diol in a process for forming picture-like images, process for preparation of fibrous polymers, and as hardenable materials formed by irradiation, respectively. However, no mention is made of thermochromic properties of the materials.
It has been found that certain acetylenic monomers, containing at least one --C.tbd.C--C.tbd.C-- group, form polymers upon thermal annealing or exposure to radiation which exhibit thermochromic behavior. The thermochromic behavior is unpredictable and has been found to occur in certain narrow classes of polyacetylenic compounds.